Fuel-vapor emission control system for an automotive engine

The present invention relates to a fuel-vapor emission control system using a charcoal canister for an automotive engine.

There is provided a fuel-vapor emission control system in the automotive engine for preventing air pollution. When the engine operation is stopped, evaporated fuel in a fuel tank and a carburetor is captured and adsorbed by activated charcoal in a charcoal canister of the control system. While the engine is running, the fuel-vapor stored in the canister is purged by intake-manifold vacuum to flow back to the intake system for combustion. A purge control of the canister is provided having a purge control valve provided on the canister which is adapted to be opened by vacuum at a port formed in an intake passage at part throttle operation. The port is positioned just above a throttle valve when it is closed, and hence the fuel-vapor in the canister is delivered together with air into the intake system. Therefore, at starting of a vehicle, when an accelerator pedal is slightly depressed, a large amount of purging takes place. A large amount of vapor by the purging enriches the air-fuel mixture, which will cause the engine to stall.

In order to remove such disadvantages, there is provided a fuel-vapor emission control system for limiting the amount of purging when starting a vehicle. For example, Japanese utility model publication No. 56-54375 discloses a system in which a solenoid operated valve is provided in a purge line and the solenoid is connected in series to a vehicle speed sensor and to a vacuum switch which detects an opening degree of a throttle valve. However, in such a system, purging does not occur at the starting, and it is adapted to take place only at a predetermined vehicle speed. As a result, a decrease of the amount of purging causes an overflow of fuel-vapor from the canister.

An object of the present invention is to provide a fuel-vapor emission control system which effectively controls the amount of purging according to engine operating conditions so as to prevent the overflow of fuel-vapor and stalling of an engine at starting of a vehicle.

According to the present invention, there is provided a fuel-vapor emission control system for an automotive engine mounted on a vehicle, the system comprising a canister having a vacuum operated surge control valve, communicating with a float chamber of a carburetor and with a fuel tank for purging fuel-vapor, a passage for communicating a port provided in the carburetor with a vacuum chamber of the vaccum operated purge control valve so as to apply manifold vacuum to the vacuum chamber at partial-throttle operation. Parallel purge lines are provided for communicating the canister with an intake manifold of the engine. A solenoid operated valve is provided in one of the purge lines for controlling the purging of the fuel-vapor. The solenoid operated valve is opened by a signal of a vehicle or engine speed sensor so as not to stall the engine.

The other objects and features of this invention will be apparently understood from the following description with reference to the accompanying drawings.

A single FIGURE shows a schematic view of a fuel-vapor emission control system according to the present invention.

Referring to the drawing, an internal combustion engine 3 is provided with a carburetor 1 communicated with an intake manifold 2 of the engine. A float chamber 4 of the carburetor 1 and a fuel tank 5 are communicated with a canister 8 by fuel-vapor induction lines 6 and 7 respectively for adsorbing and storing fuel-vapor. The canister 8 is filled with particles of activated charcoal and has a purge control valve 12 provided on the upper portion thereof. The purge control valve 12 comprises a vacuum chamber 13 defined by a diaphragm 14 and a valve port 15 normally closed by the diaphragm 14. A port 10 formed in the carburetor 1 is communicated with the vacuum chamber 13 by a vacuum passage 11. The port 10 is located just above the upward swinging end of a throttle valve 9 in its closed position so that it is exposed to induction vacuum when the throttle valve 9 is partly opened. A purge line 18 having parallel purge lines 19 and 19a, which have orifice-type restrictors 16 and 17 respectively, is provided to communicate the valve port 15 with the intake manifold 2. A solenoid operated valve 21 is provided in the purge line 19 and operated by a signal from a vehicle speed sensor 20. The vehicle speed sensor 20 is adapted to generate the signal to open the solenoid valve 21 when the vehicle speed exceeds a predetermined value.

When the engine operation is stopped at a high temperature, especially in summer, a large amount of fuel evaporates in the float chamber 4 and fuel tank 5. The fuel-vapor flows into the canister 8 passing through the fuel-vapor induction lines 6 and 7, so that fuel-vapor is adsorbed and stored by the charcoal. In idling or deceleration state after the engine is started, the throttle valve 9 is closed so that the atmospheric pressure is applied to the vacuum chamber 13 of the purge control valve 12 through the port 10 and the vacuum passage 11. Accordingly, the diaphragm 14 is deflected to close the valve port 15 and the purging does not take place. When the throttle valve 9 is opened over the port 10, the manifold vacuum is applied to the vacuum chamber 13 through the port 10 and the passage 11. Hence the diaphragm 14 of the purge control valve 12 is deflected upwardly to open the valve port 15 so that the valve port 15 communicates with purge lines 18, 19 and 19a. By the manifold vacuum, atmosphere is sucked into the canister 8 through bottom holes and through the charcoal to purge the fuel-vapor from the charcoal in the canister 8 which passes to the intake manifold.

When starting, since the vehicle speed is lower than the predetermined value, the solenoid valve 21 provided in the purge line 19 is not excited so that the purge line 19 is closed by the valve 21. Therefore, the fuel-vapor purged from the canister passes through only the purge line 19a in which the orifice 16 operates to restrict the flow of fuel-vapor for preventing stalling of the engine. When the vehicle speed exceeds the predetermined value, the solenoid valve 21 is opened by the signal from the speed sensor 20. Consequently, fuel-vapor flows through both purge lines 18, 19 and 19a. Thus, a sufficient amount of purging takes place.

The vehicle speed sensor of the present invention can be replaced with an engine speed sensor. The system of the present invention is applicable to a system in which a thermo valve is provided on the vacuum passage 11 for high idling speed in cold engine state.

In accordance with the present invention, since the purge control valve is connected to two purge lines having orifice-type restrictors for the fuel-vapor flow control and the solenoid operated valve is provided on one of the purge lines so as to be operated by the vehicle speed sensor, the amount of purging is controlled according to the vehicle speed. Therefore, the stalling of the engine and fuel-vapor overflow can be prevented.

While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.